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D. R. Hay

Abstract

No abstract available.

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C. L. Ting
and
D. R. Hay

Abstract

Measurements on wind and temperature fields near the ground as reported by Swinbank and Dyer are re-examined. Through the use of the free convection wind and temperature profiles, H and u * as derived by the present authors have accuracies that are comparable to or better than those obtained earlier through the use of the exponential wind profile and the integrated KEYPS profile.

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C. L. Ting
and
D. R. Hay

Abstract

No abstract available.

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R. L. Johnson
,
D. E. Janota
, and
J. E. Hay

Abstract

During the spring-summer of 1979, six lightning warning devices were evaluated in a side-by-side comparison study at three test sites. Stock commercial devices were selected based upon distinct concepts of operation. The devices tested included a sferics counter, a corona point, a radioactive probe, a field mill, an azimuth/range locator and a triangulation locator. The test sites were chosen to provide varied thunderstorm conditions: 1) San Antonio, Texas (cold air advection), 2) Kennedy Space Center, Florida (localized surface heating) and 3) Langmuir Laboratory, New Mexico (orographic effects). The evaluation parameters were advance warning time, time to clear after hazard, alarm reliability, and false alarm and failure to alarm probabilities. The triangulation locator provided the best overall performance; however, all systems indicated a need for improvement in the failure to alarm rate.

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N. Stark
,
A. E. Hay
,
R. Cheel
,
L. Zedel
, and
D. Barclay

Abstract

A prototype wideband coherent Doppler profiler (MFDop) was tested for measuring bedload velocity of different gravel and coarse-sand-sized fractions (d = 1–32 mm) in the laboratory. The sediment was spread out on a smooth-surface tray, and motion was initiated by tilting the tray at angles of α = 20°–39° from the horizontal. Particle velocities downslope (u), cross slope (υ), and vertical to the tray (w) were determined for different MFDop parameter settings, such as monostatic/bistatic configuration, acoustic beam angle, and pulse length. Video observations of bed particle velocity were made for comparison to the acoustic measurements. Velocities estimated using the MFDop equal to, on average, 71%–74% of the velocities determined using the video observations. Standard deviations ranged from 21% to 35%, including observed irregular motion. Three stages of sediment motion were observed: (i) single particles moving with u ≤ 5 cm s−1, (ii) varying motion of particles and particle groups with predominantly 5 cm s−1u ≤ 20 cm s−1, and (iii) fast sheetlike motion with u ≥ 20 cm s−1. The cross-slope velocity υ and the vertical velocity w were significantly smaller than u, hinting at slipping as the major particle motion rather than rolling or saltation. Comparisons between MFDop and video-determined velocities showed good agreement. Standard deviations for the MFDop velocity estimates ranged from 22% to 35%. The trials with different gravelly sediments and coarse sand revealed a significant influence of grain size, as well as grain shape impacting the initiation of sediment transport and transport velocities.

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Naoki Mizukami
,
Martyn P. Clark
,
Ethan D. Gutmann
,
Pablo A. Mendoza
,
Andrew J. Newman
,
Bart Nijssen
,
Ben Livneh
,
Lauren E. Hay
,
Jeffrey R. Arnold
, and
Levi D. Brekke

Abstract

Continental-domain assessments of climate change impacts on water resources typically rely on statistically downscaled climate model outputs to force hydrologic models at a finer spatial resolution. This study examines the effects of four statistical downscaling methods [bias-corrected constructed analog (BCCA), bias-corrected spatial disaggregation applied at daily (BCSDd) and monthly scales (BCSDm), and asynchronous regression (AR)] on retrospective hydrologic simulations using three hydrologic models with their default parameters (the Community Land Model, version 4.0; the Variable Infiltration Capacity model, version 4.1.2; and the Precipitation–Runoff Modeling System, version 3.0.4) over the contiguous United States (CONUS). Biases of hydrologic simulations forced by statistically downscaled climate data relative to the simulation with observation-based gridded data are presented. Each statistical downscaling method produces different meteorological portrayals including precipitation amount, wet-day frequency, and the energy input (i.e., shortwave radiation), and their interplay affects estimations of precipitation partitioning between evapotranspiration and runoff, extreme runoff, and hydrologic states (i.e., snow and soil moisture). The analyses show that BCCA underestimates annual precipitation by as much as −250 mm, leading to unreasonable hydrologic portrayals over the CONUS for all models. Although the other three statistical downscaling methods produce a comparable precipitation bias ranging from −10 to 8 mm across the CONUS, BCSDd severely overestimates the wet-day fraction by up to 0.25, leading to different precipitation partitioning compared to the simulations with other downscaled data. Overall, the choice of downscaling method contributes to less spread in runoff estimates (by a factor of 1.5–3) than the choice of hydrologic model with use of the default parameters if BCCA is excluded.

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I. A. Renfrew
,
G. W. K. Moore
,
J. E. Kristjánsson
,
H. Ólafsson
,
S. L. Gray
,
G. N. Petersen
,
K. Bovis
,
P. R. A. Brown
,
I. Føre
,
T. Haine
,
C. Hay
,
E. A. Irvine
,
A Lawrence
,
T. Ohigashi
,
S. Outten
,
R. S. Pickart
,
M. Shapiro
,
D. Sproson
,
R. Swinbank
,
A. Woolley
, and
S. Zhang

Greenland has a major influence on the atmospheric circulation of the North Atlantic-western European region, dictating the location and strength of mesoscale weather systems around the coastal seas of Greenland and directly influencing synoptic-scale weather systems both locally and downstream over Europe. High winds associated with the local weather systems can induce large air-sea fluxes of heat, moisture, and momentum in a region that is critical to the overturning of the thermohaline circulation, and thus play a key role in controlling the coupled atmosphere-ocean climate system.

The Greenland Flow Distortion Experiment (GFDex) is investigating the role of Greenland in defining the structure and predictability of both local and downstream weather systems through a program of aircraft-based observation and numerical modeling. The GFDex observational program is centered upon an aircraft-based field campaign in February and March 2007, at the dawn of the International Polar Year. Twelve missions were flown with the Facility for Airborne Atmospheric Measurements' BAe-146, based out of the Keflavik, Iceland. These included the first aircraft-based observations of a reverse tip jet event, the first aircraft-based observations of barrier winds off of southeast Greenland, two polar mesoscale cyclones, a dramatic case of lee cyclogenesis, and several targeted observation missions into areas where additional observations were predicted to improve forecasts.

In this overview of GFDex the background, aims and objectives, and facilities and logistics are described. A summary of the campaign is provided, along with some of the highlights of the experiment.

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Shelley D. Crausbay
,
Aaron R. Ramirez
,
Shawn L. Carter
,
Molly S. Cross
,
Kimberly R. Hall
,
Deborah J. Bathke
,
Julio L. Betancourt
,
Steve Colt
,
Amanda E. Cravens
,
Melinda S. Dalton
,
Jason B. Dunham
,
Lauren E. Hay
,
Michael J. Hayes
,
Jamie McEvoy
,
Chad A. McNutt
,
Max A. Moritz
,
Keith H. Nislow
,
Nejem Raheem
, and
Todd Sanford
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